PROJECT SUMMARY The bacterium Burkholderia pseudomallei causes the human disease melioidosis and is currently the third leading cause of death in Northeast Thailand. Despite the increasing prevalence of melioidosis, mechanisms of B. pseudomallei pathogenesis remain poorly understood and treatment options are limited. This proposal is focused on a cytotoxic B. pseudomallei polyketide, malleilactone, which is important for B. pseudomallei pathogenesis in several infection models. Malleilactone is not produced in normal laboratory conditions, but its production can be elicited by certain antibiotics such as trimethoprim. Some of the antibiotics that induce malleilactone production are among the few available options to treat melioidosis. Our long-term goal is to define the underlying mechanisms of B. pseudomallei virulence, and use this information to identify novel therapeutic interventions to treat this challenging human disease. Here we propose to (i) synthesize and determine the mode of action of malleilactone, (ii) determine the spatial and temporal pattern of malleilactone expression and cytotoxicity in a murine model of melioidosis, and (iii) elucidate the regulatory pathway that triggers induction of the malleilactone biosynthetic genes using both directed and global approaches. These results are essential to gain a mechanistic understanding of how malleilactone increases B. pseudomallei pathogenesis and will provide insight into how this versatile pathogen has evolved the ability to adapt to different environments. In addition toxic polyketides are emerging as a broadly ubiquitous and poorly understood class of virulence factors in many pathogens, and we anticipate that B. pseudomallei and the robust animal models available for this species will provide insight into polyketide virulence mechanisms in a broader sense. Elucidating the underlying mechanisms that lead to malleilactone-dependent virulence will provide critical new information on B. pseudomallei pathogenesic mechanisms, and is an important step towards improving the currently limited treatment options for this devastating disease.